This invention relates to electric motors and, in particular, to an improved electric motor having bridge-type magnetic circuits.
A general type of synchronous motor includes a multipolar stator field, a source of alternating flux and a source of excitation flux. Many synchronous motors of this type exhibit significant magnetic losses which are undesirable. Such losses usually result in the development of relatively small torque, thus requiring increased flux generation.
To overcome many of the disadvantages of such synchronous motors, a motor has been proposed including a bridge-type magnetic circuit. Such motor comprises an elongated aramture, and a stator structure including a coil and having two pole pieces. Both the stator and rotor have salient poles which are arranged such that the opposite ends of the rotor are subjected to magnetic potentials derived from the stator magnet. These magnetic potentials vary sinusoidally in accordance with the angle of rotation of the rotor; and the variation of the potential at one end of the rotor is opposite in phase to the variation of the potential at the other end. Consequently, an alternating magnetic flux of zero average value passes through the rotor axis when the rotor rotates, independently of the flux produced by the coil. The flux from the coil is superposed in the axial direction of the rotor and passes through the stator plates of the stator structure, but without passing through the permanent magnet. In some motors of this type two such magnetic bridge circuits are connected in parallel.
In a further proposal for a synchronous motor having bridge-type magnetic circuits, the bridge-type magnetic circuits include pairs of radially disposed magnetically permeable plates. The radial plates are positioned about the rotor axis.
These prior bridge-type motor structures are generally expensive to manufacture and are relatively complex in design.